Vaccination reporting differences
Statistics producers can make many different reports. Those reports can have distinctions, dependent on analytical choices. I look at two reporting differences for Covid-19 vaccinations in England and Wales.
Why do the daily and weekly NHS England stats differ?
NHS England produce two sets of reports on vaccinations: by day and by week. The latest weekly report goes up to 30th May 2021. These extensive analyses show vaccinations by gender, age, ethnicity and more.
We can compare those figures to the daily report for the same date. Daily reports contain only headline statistics:
- Daily: 32,938,496 first doses and 21,719,461 second doses.
- Weekly: 32,756,725 first doses and 21,609,411 second doses.
First, there is a timing difference on data extraction. The weekly report is for vaccinations administered between 8th December and 30th May. Analysts ran that extract on 1st June. That includes vaccinations done on 30th May, but reported a day later. As the daily report states:
Not all vaccinations administered up to this date will be included in these figures.
Second, there are exclusions in the weekly report. These reports only include living residents with an NHS number. That means numbers of vaccinated people could decrease between weekly reports.
Why does vaccination coverage for Wales differ between reports?
Public Health Wales have a Tableau Public dashboard for Covid-19 statistics. The public health agency also produce weekly reports for vaccination coverage. Public Health England also report on Welsh vaccinations through their main dashboard. These figures are up to 30th May:
- Public Health Wales: 2,112,620 first doses, or 80.5% of adults (18+).
- Public Health England: 2,146,071 first doses, covering 85.1%.
There is another dating difference. The PHE dashboard shows Welsh vaccinations by reporting date. The PHW report is by vaccination date:
Not all data for vaccinations are entered electronically into WIS at the point of vaccination and there will be paper forms yet to enter for vaccinations given up to Sunday.
The headline PHW statistic is similar to PHE: 2,146,126 first doses. The coverage numbers in later tables in the same report exclude people who later died. There were also around 19,300 people who live outside Wales getting a dose there.
There is the Covid-19 Welsh Immunisation System (WIS), which records vaccinations. In that report, the WIS denominator for Welsh adult residents was 2.63m. In contrast, Public Health England uses the Office for National Statistics estimate for Wales of 2.52m. Their dashboard calculates UK-wide estimates too, with consistency across the four nations.
It is important to recognise reporting differences in statistics.